In a solidarity system, all layers are important. But it is true that the 1st and 2nd layer would be useless if, in unfavorable conditions, rain or snow soaks them. This is why the third layer is so important in the system: because its function is especially necessary when things get uglier, and we need more help.
In the early days of the system, third layers were limited to waterproof, breathable, and windproof membrane jackets. And although it is true that, of the 3 layers, it is perhaps the one that has changed the least, if it has undergone changes.
As we explained in the article How to choose your 2nd layer, today we could rather talk about the 2.5-3 layer system. And this has freed the third layer of part of its function.
What does this 2.5 system consist of?
Basically, the 1st layer continues to fulfill its function, but the old thick 2nd layer fleeces, in many cases, have been divided into 2 garments (we recommend to see article on 2nd layer for more information):
a fine first, micropolar, or powerstretch
and a second that can be a thin layer with filling, in what we could call 2.5 layers. This layer provides heat, cuts the wind, and is very agile.
In this way, in many cases, especially in athletic activities, the 3rd layer is used only in cases of rain, snow, very cold, very windy, since the 2nd layer is part of its old role against the elements.
It is an evolution that was born with softshells: 2nd outer layer or 3rd layer more comfortable and with greater thermal protection than a traditional membrane jacket (let's not forget that it protects from rain and wind, but it is not a heat layer). A garment that joined the 2nd layer and the 3rd layer.
How to classify the third layers?
Hardshell: they are the traditional waterproof, breathable and windproof jacket, without heat protection, with a Gore-Tex type membrane or similar.
They remain fundamental and irreplaceable when things get ugly. At other times, its use is less because of what has been said about softshells and the 2.5-layer system, but -as we say- they are still essential.
Softshell: They were the first step towards opening up new possibilities for the layer system. As we say, they can be considered as a mixture between the 2nd and 3rd layer. There are some that tend towards the 2nd layer because of their design, and others that are hardly distinguishable from a 3rd layer if we don't examine their specification sheet. The latter are very good as a third layer in cold winter conditions, in which if it precipitates it will be in a solid form, by gaining comfort, thermal protection, elasticity, and having adequate protection against snow and wind.
They were born from a realization: if the waterproof and breathable jacket are prepared to withstand the worst conditions, a jacket can be created that increases breathability and comfort -for its fabric, elastic and more pleasant- for when such a high degree of waterproofing is not necessary, such as in situations of fine rain, or snow and ice.
Although it is true that the fine polar-2nd heat layer combination has relegated them to the background, they are still very good when you need very tear-resistant garments, etc., such as freeriding or mountaineering.
Hybrid shells: The most exposed parts are made with Hardshell, and the least with Softshell. They protect in case of very bad conditions, but they provide the comfort, breathability and resistance of the softshell.
Ultralight: They are waterproof and breathable. At first they were born as a complement to softshells. You were protected with your softshell, and in case of severe deterioration, you could take out the ultralight jacket and put it on. It took almost no weight or space in the backpack.
It remains one of its uses. But it was soon discovered that they were the perfect replacement for the plastic raincoat in the summer, and an excellent garment for new very athletic activities and faster mountaineering.
Actually, nowadays, quality 3rd layer jackets, made with Gore-Tex Pro or similar, can be almost as light according to their design as an ultralight jacket from before, adding resistance.
Filled: In the layer system, the second layer is responsible for retaining heat. If we use padded third layer garments (waterproof and breathable membrane type plus padding), we lose the versatility of the system by combining the protective layer with the heat. Its use in the mountains is not recommended, except for very extreme situations (winter arctic, etc.). If used in cross-country skiing.
Do not confuse this type of garment with the second layers of the 2'5 system, which provide protection against the elements.
How to choose?
It depends on the use and conditions.
The first thing to consider in a traditional waterproof and breathable third layer is its cut: there are more athletic ones, for mountaineering, designed to be worn with harness and material (they are usually shorter), and there are other uses, with greater protection.
Most will opt for a versatile range, which can be used with a harness, but without reaching the minimalism and adaptation required by the most technical.
If we are going to do alpine activities in winter, we need a waterproof and breathable jacket that can be combined with the layers below and that protects us. In this case, if we think that we are going to use total waterproofness and choose softshell, it is better that it can be used under the third layer. But if we think that we will only use the jacket in conditions of solid precipitation, a third layer softshell can do us good.
If our activities are going to be more athletic, such as cross-country skiing, we can opt for the combination of 2.5 layers and a light jacket.
For out of winter season and mountaineering, we can use a light jacket perfectly, either ultralight materials, a quality 3 layers and light weight. Actually, this garment (3 layers light, for example from Goretex Pro) would be the ideal: low weight for all-year and athletic activities, great protection for alpine activities.
For occasions when we prefer resistance, some heat capacity, comfort and greater breathability, and protection against soft elements (fine rain, etc.), a softshell will be ideal.
As with the trunk, the third mountain layers must protect from the elements. However, there is some difference:
It is not necessary to shelter the legs as much as the rest of the body
More agility is needed
In cold and winter mountaineering situations, a very comfortable softshell pants are usually worn, which can be complemented by some inner tights, and with a waterproof and breathable trousers, which we wear well throughout the activity (in this case, the softshell pants would be a 2nd layer), we carry well in the backpack in case the conditions get very wet (in this case, the softshell would be used as a 3rd layer).
There are hybrid pants, which come to be softshell with waterproof and breathable material in the exposed areas (front leg, bottom).
In good weather situations, we will wear trekking pants, a 3-season thin softshell mountaineering pants, and if we are going to be in the high mountains, we can wear an ultralight waterproof and breathable overpant in case of rain with low temperatures.
It is convenient, in all cases, that if we are going to use the third waterproof and breathable layer according to the weather, it has a side zipper opening, to facilitate putting on and removing boots on the go.
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